Glomerulonephritis or glomerular nephritis (“GN”) is a renal disease which is characterized by inflammation of the glomeruli or capillary loops of the kidney. It is a pathologic process associated with a number of diverse underlying diseases. The condition occurs in acute, sub-acute and chronic forms and also secondary to an infection. The former conditions, where a concurrent illness cannot be found, are generally referred to as idiopathic glomerulonephritis. The latter conditions are generally referred to as secondary GN. Whatever the underlying cause, immune complexes form and result in a series of events leading to glomerular injury and loss of renal function, proteinuria and ultimately, in some cases, renal failure.
Nephritis is an inflammation of the kidney, which may be a focal or diffuse proliferative or destructive disease involving the glomerulus, renal tubule or the kidney interstitial (or connective) tissue. The most common form of nephritis is glomerulonephritis. Nephritis may progress through a number of stages ending in end-stage kidney disease or end-stage renal failure.
Renal failure results from the inability of the kidney to maintain its normal functions. As a result, metabolic waste products and metabolites accumulate in the blood. These waste products and metabolites may adversely affect most bodily systems. Disturbances in the maintenance of fluid and electrolyte balances are characteristics of renal failure.
Acute renal failure may occur suddenly due to trauma, infection, inflammation or exposure to nephrotoxic substances. This condition may result in dehydration, hypotension and circulatory collapse. Acute renal failure is frequently segregated into three categories: (1) pre-renal failure, which is associated with decreased renal blood flow; (2) intra-renal failure, which is associated with ischemia and toxins; and (3) post-renal failure, which results from obstruction of urine flow.
Chronic renal failure involves a progressive loss of kidney function that may eventually progress to end-stage renal disease or failure. At inception, chronic renal failure begins as a diminishing kidney function, without appreciable accumulation of metabolic waste products in the blood. As the glomerular filtration rate slows due to inflammation, waste products begin to accumulate. The disease progresses to uremia due to low kidney function, and high levels of protein end products start to accumulate and impair bodily functions. Common causes of chronic renal failure include: inflammation, infection, urinary tract obstruction and certain systemic diseases and toxicities, including hypercalcemia, lupus erythematosus, diabetes mellitus and hypertension.
End-stage renal disease is marked by irreversible chronic renal failure. Serum creatinine and blood urea nitrogen levels continue to rise and the resulting uremia impairs all bodily systems. The kidney can suffer permanent and almost complete loss of function on the order of 10% or less of normal kidney function. One cause of end-stage kidney disease is glomerulonephritis. Other causes include those mentioned for chronic renal failure.
Glomerulonephritis may arise as a result of a biological insult to the immune system. Foreign substances may adhere to the basement membrane and cause an immune response resulting in the production of antibodies. These antibodies may combine with the foreign substances to cause immune complexes that become deposited on the walls of the tiny glomerular capillaries, resulting in damage to the nephron. Alternatively, in some individuals the immune system can create autoantibodies which are immunoglobulins that may attack kidney cells resulting in a so-called autoimmune response. If proteins in the body are altered, an autoantibody response may ensue because the autoantibodies recognize the altered proteins as non-self. These autoantibody-protein complexes may likewise be deposited on the basement membrane of the glomerulus causing a disruption of the functioning of the nephron.
Glomerulonephritis is a common cause of proteinuria in dogs and may be either the idiopathic or secondary form of the condition. In the latter situation, the condition may develop secondary to neoplasia, inflammatory diseases, endocrine malfunctions, infections or familial nephropathies. As in humans, GN in dogs is mediated immunologically, involving immunoglobulins and complement factors in the body of the animal. Injury occurs within the glomeruli of the kidney resulting in morphological changes to the glomeruli. Eventually the injury is irreversible and leads to malfunction of the nephrons.
It is generally accepted in the scientific community that the regulation of gene expression plays a key role in the development of some diseases or conditions that affect an animal's health and well being. Similarly, a differential expression of genes is one factor in the development of such diseases and conditions and the evaluation of gene expression patterns has become widely recognized as important to understanding the development and control of such diseases and conditions at the molecular level. To advance the understanding of genes and their relationship to disease, a number of methods have been developed for studying differential gene expression, e.g., DNA microarrays, expressed tag sequencing (EST), serial analysis of gene expression (SAGE), subtractive hybridization, subtractive cloning and differential display (DD) for mRNA, RNA-arbitrarily primed PCR (RAP-PCR), real-time PCR (RT-PCR), representational difference analysis (RDA), two-dimensional gel electrophoresis, mass spectrometry, and protein microarray based antibody-binding for proteins.
Due to the complexity of the biological pathways implicated in renal disease and the inherent molecular interactions and intercellular signaling processes, it is highly desirable to understand at a genetic level the interactions that are taking place. Detection of dysregulated genes in the early stages of loss of renal function in canines is helpful in understanding the biology of renal disease, especially glomerulonephritis on a genome-wide basis. The fact that gene dysregulation may be detected at an early stage of disease development in animals subjected to repeated ischemic injury is helpful in designing methods for diagnosing of, and devising and monitoring a treatment plan for, an abnormal loss of kidney function, renal failure, reduced glomerular filtration rate or glomerulonephritis, in a canine.
A more detailed understanding of the biological pathways involved through gene expression profiling will aid in the development of diagnostic procedures, reagents and test kits as well as salutary pharmaceutical, nutraceutical and nutritional (dietary) interventions in the disease pathways. These approaches may enable early detection and potentially prevention or treatment of the underlying kidney disorder, particularly glomerulonephritis, as well as in monitoring the prognosis of early stage renal failure and glomerulonephritis, especially in canines. Dysregulated genes involved in the pathology of such disorders may serve as important biomarkers for diagnosis and potentially prevention or treatment of the disorder and to optimize selection of appropriate pharmaceutical, nutraceutical and nutritional (dietary) interventions.
The level of gene expression and/or the determination of the level of functioning of an expressed gene product in a canine may be used to select an appropriate agent for therapeutic or prophylactic use. This data may be employed by the skilled worker in selecting appropriate drugs as agents for the prevention or treatment of renal diseases in canines through gene expression profiling. Gene expression data and analysis may also be used to select nutritional compositions, dietary supplements, and nutraceuticals having a salutary effect on kidney performance by utilizing biomarkers indicative of a healthy state of kidney functioning.
Only very limited work has been done to date in screening the canine genome for gene expression profiles in connection with the diagnosis of diseases in dogs. Certain work employing animal models has utilized cDNA array technologies to screen for gene expression in renal tissues associated with renal disease.
Studies in healthy populations of canines versus populations having a disease such as a kidney disease and loss of kidney function as described in this specification have not been extensively conducted. Little data is available with respect to the expression profile of the canine genome, especially with respect to the development of renal diseases in canines over time. Gene expression data contained in this specification identifies the genes associated with renal function in dogs. Such gene expression data enables development of compositions and methods for diagnosing of, devising and monitoring a treatment plan for, and monitoring the status of, a kidney disorder characterized by an abnormal loss of renal function, renal failure, reduced glomerular filtration rate or glomerulonephritis, in a canine, wherein the kidney disorder is detectable by utilizing at least one relevant biomarker isolated and measured from a biological test sample taken from such canine.
Gene expression data contained in the specification and examples enables a variety of desirable inventions based on the gene expression profiles described in the specification and examples of this patent application. The data permits identification and quantification of gene expression products as biomarkers of disease prevention, identification and treatment of the underlying renal disease. Gene expression data elicited as a result of the practice of the methods of the invention also permits monitoring the progression of such renal disease. These inventions further include genetic testing to identify susceptible subpopulations of animals likely to be afflicted with such renal disease, to identify optimal diets for the prevention or treatment of such renal diseases, to identify pharmaceutical, nutraceutical and nutritional (dietary) interventions based on the findings set forth on this specification in order to treat the underlying renal diseases. The inventions also include biomarkers for early disease detection, targeted therapeutics, diagnostic reagents and kits for the analysis of tissue and blood samples from canines susceptible to or having such a renal disease.